The major goals of our research is to study in detail the mechanism of hormone induced receptor clustering and the relationship between receptor mobility, aggregation, internalization and hormone responsiveness. Our goals are divided into three major directions: 1. Elucidation of the mechanism of hormone induced receptor clustering. We will evaluate the rate of the aggregation process by kinetic studies in which we will examine the effect of hormone concentration, temperature and time of occupancy. The formation of receptor microaggregates will be revealed by measurement of their rotational diffusion coefficients and by measuring the change in non-radiative energy transfer between receptors labeled with two different fluorophores. We will examine the possibility that the enzyme transglutaminase in involved in the process of hormone induced receptor clustering. 2. Characterization of the relationship between hormone receptor aggregation and hormone action. We will examine the effect of changes in the viscosity of the lipid matrix by enriching it or depleting its cholesterol content and also the effect of various pharmacological agents on receptor mobility, clustering and hormone response. 3. Characterization of the fate of the bound hormone: hormone internalization. We will study the role of membrane coated regions in the mechanism of hormone patching the endocytosis. We will use antibodies against clathrin together with fluorescent-hormones and employ fluorescence microscopy. Furthermore we will prepare ferritin conjugates of EGF and NGF and employ electron microscopy to localize their intracellular location.